Paper-plastic laminate sheeting

ABSTRACT

A paper-plastic laminate sheeting capable of being converted by conventional equipment into envelopes, grocery bags and other dilatable container products that initially are in a flat state and are normally made of paper. The sheeting is composed of a paper facing sheet cold-laminated by means of a water-based adhesive to a reinforcing film of synthetic plastic material, such as polypropylene. The film is oriented to impart exceptional tear and burst strength characteristics to the resultant waterproof product. The product, whose exterior surface is formed by the paper facing sheet, is readily printable. For some applications, a second paper facing sheet is cold-laminated to the other side of the film to produce a three-ply laminate sheeting whose exposed surfaces are readily printable and can accept conventional adhesives.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/167,268filed Jun. 10, 2002, now U.S. Pat. No. 6,652,984, which is a division ofapplication Ser. No. 09/781,181 filed Feb. 12, 2001, now U.S. Pat. No.6,706,388, which is a continuation of application Ser. No. 09/258,766,filed Feb. 26, 1999, now U.S. Pat. No. 6,235,386, which is acontinuation of application Ser. No. 08/209,405 filed Mar. 14, 1994, nowU.S. Pat. No. 5,962,099, which is a continuation of application Ser. No.08/057,963 filed May 4, 1993, now abandoned, which is a division ofapplication Ser. No. 07/818,544 filed Jan. 9, 1992, now U.S. Pat. No.5,244,702.

BACKGROUND OF INVENTION

1. Field of Invention

This invention relates to paper-plastic and paper-plastic-paperlaminates in the form of sheeting which is capable of being convertedinto a self-closing package or other material such as envelopes, bagsand other dilatable container products which initially are in a flatstate and are normally made of paper. In these laminates, a paper facingsheet is cold-laminated to an oriented film of synthetic plasticmaterial, or two paper sheets are cold laminated to the film.

2. Status of Prior Art

The sheeting traditionally used in making envelopes, grocery bags andother types of dilatable container products which initially are in aflat state is paper. Paper is a semi-synthetic material made bychemically processing cellulose fibers.

Apart from its low cost, an important advantage of paper is that it canbe converted into envelopes and other types of dilatable containerproducts by means of high speed equipment that functions to cut and foldthe sheeting into the desired configuration, the folds and flaps of theproduct being bonded together, where necessary, by standard low-costadhesives. Another advantage of paper in this context is that it canreadily be printed and colored, using standard inks for this purpose.

But such paper products suffer from several disadvantages, for they arecharacterized by low tear and burst strength, and are by no means waterresistant; for unless coated, paper is highly absorbent.

Also well known in the art are plastic-coated cellulosic papers, thesebeing used chiefly in children's books, posters, signs and shippingtags, and for other purposes demanding resistance to hard wear and tooutdoor exposure. However, such plastic-coated papers lack high tear andburst strength. Also low in strength are special purpose coated paperscovered on one or both sides with a suspension of clays, starches, rosinor wax, or a combination of these substances.

To overcome the drawbacks of paper-fabricated dilatable containerproducts, in recent years such products have been made of TYVEC or otherpolymeric synthetic plastic sheeting. The resultant products not onlyhave a tear and bursting strength far superior to paper, but they arealso waterproof.

However, TYVEC and similar synthetic plastic sheeting is difficult toconvert into envelopes and other dilatable container products usinghigh-speed equipment of the type mainly suitable for paper. As aconsequence, production scrap rates can run as high as thirty percent,thereby raising the cost of manufacturing these products. Moreover, suchplastic sheeting has a low chemical affinity for standard adhesives;hence in the case of envelopes, one must then use a special and morecostly adhesive on the flaps. And such plastic sheeting also has a lowaffinity for standard printing inks, and the products, therefore, demandspecial printing inks for this purpose.

SUMMARY OF THE INVENTION

The invention relates to a flexible paper-plastic laminate sheetingcapable of being converted by conventional equipment into envelopes,bags and other dilatable container products normally made of paper whichinitially are in a flat state. The laminate sheeting comprises:

(a) a first paper facing sheet having first and second surfaces; and

(b) a reinforcing film of a synthetic oriented polymer comprisingpolyethylene or polypropylene, the film having a first and secondsurfaces, one of which is treated to increase its dynes and its affinityto adhesives, the treated surface of the film being cold-laminated by awater-based adhesive to the first surface of the paper facing sheetwhereby products made from the sheeting have a printable paper exteriorand exceptional tear and burst strength.

In a preferred embodiment, a second paper facing sheet having first andsecond surfaces is cold-laminated by a water-based adhesive to the firstsurface of the second paper facing sheet to produce a non-curling,three-ply laminate sheeting having exterior surfaces of the first andsecond printable paper sheets.

To facilitate this, the second surface of the reinforcing film istreated to increase its dynes and its affinity to adhesives. In thethree ply embodiment, the reinforcing film can instead be polyester.

The invention also relates to a method of making a flexiblepaper-plastic laminate sheeting capable of being converted byconventional equipment into envelopes, bags and other dilatablecontainer products normally made of paper which initially are in a flatstate. This method comprises providing a supply of a first paper sheethaving first and second surfaces; providing a supply of a reinforcingfilm of a synthetic plastic material having first and second surfaces;orienting the film of plastic material to increase its strength;treating the first surface of the film to increase its dynes and itsaffinity to adhesives; applying a water-based adhesive to the treatedfirst surface of the film; and cold-laminating the adhesive bearingfirst film surface to the first surface of the paper sheet to form alaminate sheeting that has a paper surface and exceptional tear andburst strength.

Another embodiment of this method further comprises providing a supplyof a second paper sheet having first and second surfaces; treating thesecond surface of the film to increase its dynes and its affinity toadhesives; applying a water-based adhesive to the treated second surfaceof the film; and cold-laminating the adhesive bearing second filmsurface to the first surface of the second paper sheet to form anon-curling, three-ply laminate sheeting that has outer printable papersurfaces and exceptional tear and burst strength.

BRIEF DESCRIPTION OF DRAWINGS

For a better understanding of the invention as well as other objects andfurther features thereof, reference is made to the following detaileddescription to be read in conjunction with the accompanying drawings,wherein:

FIG. 1 illustrates a flexible, paper-plastic laminate sheeting inaccordance with the invention; and

FIG. 2 shows, in schematic form, a system adapted to produce thesheeting.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention now provides a paper-plastic laminate sheeting capable ofbeing converted by conventional equipment of the type heretofore usedwith paper, into envelopes, grocery bags and other types of dilatablecontainer products which initially are in a flat state.

This invention provides a sheeting of the above type in which a facingpaper sheet is cold-laminated to a reinforcing film of syntheticoriented plastic material, whereby the properties of the oriented filmare unimpaired and provide exceptional tear and burst characteristics.

Among the salient advantages of paper-plastic laminate sheeting inaccordance with the invention are the following:

A. The laminate is waterproof.

B. The paper facing of the laminate sheeting has a high affinity forstandard printing inks, and can readily be printed and colored.

C. A standard starch or pressure-sensitive adhesive may be used on thepaper surfaces of the laminate sheeting.

D. The laminate sheeting can be converted into other products byconventional equipment for this purpose with minimum scrap in a range ina range comparable to the scrap rate encountered in making paperenvelopes and other dilatable container products.

Also, the invention provides a system for carrying out at high speed apreferred technique for producing this laminate sheeting.

The laminate sheeting is composed of a paper facing sheet that iscold-laminated by means of a water-based adhesive to a reinforcing filmof synthetic plastic material, such as polyethylene, polypropylene orpolyester. The film is oriented to impart exceptional tear and burststrength characteristics to the resultant waterproof product. Theproduct, whose exterior surface is formed by the paper facing sheet, isreadily printable.

For some applications, a paper facing sheet is cold-laminated to theother side of the film to produce a three-ply laminate sheeting whoseexposed paper surfaces are readily printable and can accept conventionaladhesives.

The paper layer of the packaging material preferably comprises Kraftpaper and has a thickness of from about 3 to about 6 mils. The plasticfilm layer may be oriented to impart high strength thereto. A biaxialorientation is preferred for greatest strength. The plastic film layerpreferably comprises a polymer selected from the group consisting ofpolypropylene, polyethylene and polyester and has a thickness of from atleast about 0.5 to 3 mils.

The plastic film layer has a first corona-discharge treated surface.This treatment is applied to the plastic immediately before the firstcorona discharge treated surface is adhesively laminated to the paperlayer. This enables a strong bond to be achieved between the plastic andpaper to form a paper-plastic film laminate having opposed outersurfaces, one of which is paper and the other of which is plastic.

The cold lamination process enables the present laminate sheeting to bemanufactured at much higher speeds than when other adhesives, such ashot melt adhesives, are utilized, for example due to the additional timerequired for cooling of the hot melt adhesive before a secure bond isachieved. If hot melt adhesives were used instead of cold lamination forjoining the plastic film to the paper, the heat of the adhesive couldcause the film to shrink, thus causing a loss of strength. Also, the hotmelt adhesive does not achieve its final bond strength until theadhesive cools, and the plastic film can shrink before this happens.Moreover, a wrinkled or curled product often results due to thedifference in the high strength and low strength areas of the plasticfilm.

The use of cold lamination is also advantageous when an oriented orbiaxially-oriented plastic film is utilized. It is known that atelevated temperatures, such films relax and lose molecular orientationand strength. For example, when two sheets of biaxially-orientedpolyester film are seamed together, using an ultrasonically-activatedsealing bar to create internal friction and heat within the film, thefilms soften and fuse, with a resultant sealing line that is weak, suchthat the sheets then tend to tear along this line. Similar problems areencountered if an oriented film is exposed to high heat, such as if ahot melt adhesive would be used to join the film to the paper. Coldlamination utilizing a water-based adhesive is essential in order toproduce a laminate that has high strength. Any of a wide range orwater-based adhesives can be used. The paper layer absorbs the waterfrom adhesives so that a high strength lamination can be rapidlyachieved.

Another benefit of the use of a water based adhesive is that this typeof adhesive does not require the use of volatile organic solvents. Thus,adverse health and environmental effects are avoided because suchsolvents are not used. Also, additional costs for recovering ordisposing of solvents are not incurred.

Referring now to FIG. 1, shown therein in an enlarged scale is aflexible paper-plastic sheeting S in accordance with the invention.Sheeting S includes a paper facing sheet 10 whose gauge, weight andquality are appropriate to the end use for which the sheeting isintended. Thus the paper sheet may be of good quality, unbleached Kraftpaper.

Cold-laminated by an adhesive layer 11 to the undersurface of paperfacing sheet 10 is a reinforcing film 12 of synthetic plastic materialwhich is preferably transparent and is uniaxially or biaxially-oriented.Film materials suitable for this purpose are polypropylene,polyethylene, or a polyester such as MYLAR.

The tensile strength of a synthetic plastic film is substantiallyincreased by orientation which results in molecular orientation of thefilm. In the case of biaxial orientation, orientation is in both thelongitudinal and transverse directions. This is usually effected bycontrolled stretching of the unoriented film.

The tensile strength of an oriented film is seriously impaired if heatis applied thereto, for the heat acts to relax the film and cause it tolose its molecular orientation. Thus when biaxially oriented Mylar filmpanels are superposed and sealed together by heat and pressure appliedalong a line running along the panels, the film may then be easily tornalong this line.

This is the reason why in the present invention the use of hot meltadhesives to laminate a reinforcing film to the undersurface of thepaper sheet is interdicted; for to do so would seriously diminish thereinforcing characteristics of the film.

In the present invention, the plastic film is cold laminated to thepaper sheet under pressure and at room temperature by means of awater-based polyacrylate copolymer adhesive or by any other water-basedadhesive having similar bonding properties and having an affinity bothfor the paper sheet and the plastic film. Preferably, a water basedadhesive of a vinyl acetate ethylene copolymer is preferred.

Since paper tends to absorb water in the laminating process, before thepaper sheet and the film are together fed into pressure rolls andsubjected to pressure to effect lamination, the first surface of thefilm is first coated with the water-based adhesive which does notencounter the first surface of the paper sheet until these two surfacesmeet in the pressure rolls. In this way, the period during whichabsorption of the adhesive into the interior of the paper sheet can takeplace is limited.

And to render the first surface of the film more receptive to thewater-based adhesive applied thereto, it is preferably first subjectedto ionization to enhance the dynes on this surface.

FIG. 2 shows a system for carrying out a preferred technique foreffecting cold lamination of the paper sheet and a plastic orientedreinforcing film to produce a two-ply laminate sheeting.

The system includes a combining station having a pair of cooperatingpressure rolls 13 and 14 driven at high speed by a motor 15. The nipbetween the rolls is related to the thickness of the webs to belaminated and is adjusted to provide the required degree of laminatingpressure to ensure secure bonding of the webs. Fed concurrently into thenip of the pressure rolls is a web of paper 16 drawn from a supply reel17, and a web of film 18 drawn from a supply reel 19.

Reel 17 is supported at an elevated position, web 16 being drawn downfrom this reel in a vertical path and being guided by an idler roll 20into a horizontal path leading to the combining station. Film supplyreel 19 is supported at a position to feed the film in a horizontal pathtoward the combining station, reel 19 being placed well in advance ofthis station to expose a stretch of film web 18 before it enters the nipof the combining rolls.

Along the stretch just above web 18 is an ionization bar 21 whichfunctions to ionize the first surface of film web 18 to increase thedynes of the surface preparatory to the application of a water-basedadhesive thereto. Then applied onto the first surface of film web 18 bymeans of an adhesive applicator 22 is a coating of water-based adhesive.It is not essential that the coating fully cover this surface, for inpractice the roll of the adhesive applicator may take the form of aseries of rings to apply parallel strips of adhesive to the filmsurface.

Hence when the adhesive-coated film web and paper web 16 together enterthe combining station and are subjected to pressure by pressure rolls 13and 14, lamination is effected by this action. The laminated webs arethen wound on an output reel 23 driven by a motor 24. The operation ofmotors 15 and 24 are synchronized; for these motors function to draw thewebs from the supply reels.

In practice, the system may be driven by the motor to operate at a speedof 150 to 500 feet per minute, or at an even greater rate. The operatingspeed is limited by the strength of the paper web, for with a relativelythin paper web of low strength, the speed must be such as not to rupturethe paper web. Hence while the oriented film can tolerate high speeds,the speed cannot exceed that which can be tolerated by the paper web.

The two-ply paper-plastic laminate sheeting wound on output reel 23 maynow be used in exactly the same manner as a reel of ordinary paper asthe stock roll for standard equipment adapted to fabricate envelopes,bags or other dilatable paper products, by slitting, folding andwhatever other operations are dictated by the form of the product.

In some applications, a three-ply paper-plastic-paper laminate sheetingmay be desirable. In this laminate, paper sheets are cold-laminated tothe opposite sides of the oriented plastic reinforcing film. The film,which is then sandwiched between the paper sheets, serves to impartexceptional high-strength physical properties to the laminate.

In practice, a three-ply laminate can be produced in a two-stage system;the first stage being a laminate of the type shown in FIG. 2 in which apaper web is cold-laminated to one side of a film web to produce atwo-ply sheeting wound on output roll 23. In the second stage, a likelaminate is used, but in this stage, a two-ply web drawn from roll 23 isthen cold-laminated on its exposed film side to a web of paper drawnfrom a paper so that wound on the output roll of the second laminate isthe three-ply laminate sheeting.

A problem encountered with two-ply paper-film laminate sheeting is thatthis sheeting tends to curl because of the dissimilar properties of theplies. Such curling is not desirable in products such as envelopes,though it may not be objectionable in other products. But when, however,the oriented film ply is sandwiched between two like plies of paper, theresultant symmetry avoids the problem of curling.

The three-ply laminate sheeting has another important advantage, for nowboth exposed surfaces are paper. This makes it possible when thethree-ply laminate sheeting is being converted in standard equipment forthis purpose into an envelope or grocery bag in which the sheeting isslit and folded to form flaps or other elements which must be sealedtogether, to use conventional, commercially available adhesives for thispurpose, rather than the special adhesives that would be dictated if thesurfaces to be sealed together included a plastic film surface. Andbecause all exposed surfaces of the three-ply sheeting are paper, theycan be readily printed.

While there have been shown and described preferred embodiments of apaper-plastic laminate sheeting in accordance with the invention, itwill be appreciated that many changes and modifications may be madetherein without, however, departing from the essential spirit thereof.

What is claimed is:
 1. A flexible paper-plastic laminate sheetingcomprising at least one paper sheet, a reinforcing film of a syntheticoriented polymer that has at least one surface treated to increase itsdynes and make it receptive to adhesives, wherein the film is laminatedto at least one of the paper sheets by a water-based adhesive thatcontacts the treated surface of the film and has its water absorbed bythe paper sheet to effect lamination thereof.
 2. The laminate sheetingof claim 1 wherein the film has undergone molecular orientation toincrease its strength prior to lamination, and the surface of the filmis treated by ionization using corona discharge.
 3. The laminatesheeting of claim 1 wherein the film is biaxially oriented.
 4. Thelaminate sheeting of claim 1 wherein the film is polypropylene,polyethylene, or polyester.
 5. The laminate sheeting of claim 1 whereinthe water-based adhesive is a polyacrylate or vinyl acetate ethylenecopolymer.
 6. The laminate sheeting of claim 1 wherein the paper facingsheet is formed of Kraft paper.
 7. A flexible paper-plastic laminatesheeting comprising first and second paper sheets, a reinforcing film ofa synthetic oriented polymer that has first and second surfaces treatedto increase its dynes and make it receptive to adhesives, wherein thefilm is laminated to both paper sheets by a water-based adhesive thatcontacts each treated surface of the film and has its water absorbed bythe respective first and second paper sheets to effect laminationthereof.
 8. The laminate sheeting of claim 7 wherein the film hasundergone molecular orientation to increase its strength prior tolamination, and the surface of the film is treated by ionization usingcorona discharge.
 9. The laminate sheeting of claim 7 wherein the filmis biaxially oriented.
 10. The laminate sheeting of claim 7 wherein thefilm is polypropylene, polyethylene, or polyester.
 11. The laminatesheeting of claim 7 wherein the water-based adhesive is a polyacrylateor vinyl acetate ethylene copolymer.
 12. The laminate sheeting of claim7 wherein the paper facing sheet is formed of Kraft paper.
 13. A methodof making a flexible paper-plastic laminate sheeting comprising:providing a supply of a first paper sheet having first and secondsurfaces; providing a supply of a reinforcing film of a syntheticoriented polymer material having first and second surfaces; treating thefirst surface of the film to increase its dynes and its affinity toadhesives; applying a water-based adhesive to the treated first surfaceof the film; and cold-laminating the adhesive bearing first film surfaceto the first surface of the paper sheet the film such that the water ofthe adhesive is absorbed by the paper sheet to effect lamination thereofand form a product that has a paper surface and resistance againsttearing and bursting.
 14. The method of claim 13, which furthercomprises: providing a supply of a second paper sheet having first andsecond surfaces; treating the second surface of the film to increase itsdynes and its affinity to adhesives; applying a water-based adhesive tothe treated second surface of the film; and cold-laminating the adhesivebearing second film surface to the first surface of the second papersheet such that the water of the adhesive is absorbed by the paper sheetto effect lamination thereof and form a non-curling, three-ply laminatesheeting product that has outer printable paper surfaces and resistanceagainst tearing and bursting.
 15. The method of claim 14, wherein thefilm has undergone molecular orientation to increase its strength priorto lamination, and the treated first and second surfaces are achieved byionization using corona discharge.
 16. The method of claim 15, whereinthe film is biaxially oriented.
 17. The method of claim 15, wherein theorientation of the film is unchanged after cold laminating.
 18. Themethod of claim 13, wherein the film is polypropylene, polyethylene orpolyester.
 19. The method of claim 13, wherein the water-based adhesivecomprises a polyacrylate or vinyl acetate ethylene copolymer and thepaper facing sheet is formed of Kraft paper.
 20. The method of claim 14,wherein each water-based adhesive comprises a polyacrylate or vinylacetate ethylene copolymer and the paper facing sheet is formed of Kraftpaper.
 21. The method of claim 13, wherein the laminate sheeting isproduced at a speed of 150 to 500 feet per minute or greater.
 22. Themethod of claim 13, wherein the laminate sheeting is produced at ahigher speed than a paper-plastic laminate sheeting made using a hotmelt adhesive.
 23. The method of claim 13, wherein adverse health andenvironmental effects are avoided since no organic solvents are presentin the adhesive or are used during cold laminating.
 24. The method ofclaim 13, wherein the laminate sheeting is made without producing highand low strength areas of the film in order to avoid curling orwrinkling.
 25. The method of claim 13, wherein the laminate sheeting ismade without exposing the oriented polymer film to elevated temperaturesthat would cause the film to relax and lose orientation or strength. 26.A flexible paper-plastic laminate sheeting comprising, in combination,at least one paper facing sheet laminated to at least one reinforcingfilm of a synthetic oriented polymer using a water-based adhesive thatdoes not contain volatile organic solvents and that does not require theaddition of curing agents or catalysts to promote curing of theadhesive, and the surface of the film that is laminated to the paperfacing sheet is treated by ionization to enhance its affinity for thewater-based adhesive, whereby products made from the sheeting have aprintable paper exterior.
 27. The laminate sheeting of claim 26 whereinthe film is biaxially oriented.
 28. The laminate sheeting of claim 27wherein the water-based adhesive is a polyacrylate or vinyl acetateethylene copolymer.